I think I've found a quite elegant workaround: there's an existing proxy service called SuperTweet.net that offers Basic Auth over HTTP, and which seems to solve our issues. More here: http://www.supertweet.net/about/api

It's a free non-commercial service and you need not to provide your twitter account's password. Just login and authorize the app, and set a basic password of your choice. Very convenient.

I was able to quickly modify the standard TwitterClient sample to work against this proxy, and now I'm trying to publish a status update through SuperTweet. So far I get an HTTP 500 Internal Error but when I have solved it, I would publish an update and share the piece of code that works.